The present invention relates to apparatus and methods for processing substrates, such as semiconductor substrates for use in IC fabrication or glass panels for use in flat panel display fabrication. More particularly, the present invention relates to improved methods and apparatus for minimizing, during processing, arcing between a plasma-facing component associated with a plasma processing chamber and the plasma present therein and/or with another plasma-facing component.
Plasma processing systems have been around for some time. Over the years, plasma processing systems utilizing inductively coupled plasma sources, electron cyclotron resonance (ECR) sources, capacitive sources, and the like, have been introduced and employed to various degrees to process semiconductor substrates and glass panels.
During processing, multiple deposition and/or etching steps are typically employed. During deposition, materials are deposited onto a substrate surface (such as the surface of a glass panel or a wafer). For example, deposited layers comprising various forms of silicon, silicon dioxide, silicon nitride, metals and the like may be formed on the surface of the substrate. Conversely, etching may be employed to selectively remove materials from predefined areas on the substrate surface. For example, etched features such as vias, contacts, or trenches may be formed in the layers of the substrate. Note that some etch processes may utilize chemistries and/or parameters that simultaneously etch and deposit films on the plasma-facing surfaces.
The plasma can be generated and/or sustained using a variety of plasma generation methods, including inductively-coupled, ECR, microwave and capacitively-coupled plasma methods. In an inductively-coupled plasma processing chamber, for example, an inductive source is employed to generate the plasma. To facilitate discussion, FIG. 1 illustrates a prior art inductive plasma processing chamber 100, which is configured for etching in this example. Plasma processing chamber 100 includes a substantially cylindrical chamber wall portion 102 and an antenna or inductive coil 104 disposed above a dielectric window 106. Typically, antenna 104 is operatively coupled to a first RF power source 108, which may include a RF generator 110 and a RF match network 112 as shown. RF generator 110 may operate at a frequency of, for example 4 MHz. Generally speaking, the RF signals from the RF generators may be sinusoidal, pulsed, or non-sinusoidal. Dielectric window 106 is typically formed of a high resistivity dielectric material, such as high resistivity silicon carbide (SiC).
Within plasma processing chamber 100, a set of inlet gas ports (not shown) is typically provided to facilitate the introduction of gaseous source materials, e.g., the etchant source gases, into the RF-induced plasma region between dielectric window 106 and a substrate 114. Substrate 114 is introduced into chamber 100 and disposed on a chuck 116. Chuck 116 generally acts as an electrode and is operatively coupled to a second RF power source 118, which may include a RF generator 120 and a RF match network 122 as shown. RF generator 120 may operate at a RF frequency of, for example, 13.56 MHz. As mentioned, the RF signal from RF generator 120, like other RF signals from the RF generators, may be sinusoidal, pulsed, or non-sinusoidal.
In order to create a plasma, a process source gas is input into chamber 100 through the aforementioned set of inlet gas ports. Power is then supplied to inductive coil 104 using RF power source 108 and to chuck 116 using RF power source 118. The supplied RF energy from RF power source 108 coupled through dielectric window 106 excites the process source gas and a plasma 124 is generated thereby.
A focus ring 126 may be provided in certain chamber configurations. As is well known to those familiar with the plasma processing art, the focus ring helps focus the ions from plasma 124 onto the surface of substrate 114 to, for example, improve process uniformity. Focus ring 126 also protects a portion of chuck 116 from damage during processing. A plasma screen 128 may also be provided in certain chamber configurations to help contain the plasma and to prevent plasma leakage into non-active areas of the chamber, such as areas below chuck 116. Such leakage may cause premature corrosion and/or result in the inappropriate deposition of unwanted materials on certain chamber parts.
A plurality of magnets 130 may be disposed around the circumference of chamber wall 102. These magnets may be employed, for example, to facilitate control of etch rate uniformity. Chamber 100 may also be provided with different components, depending on the specific manufacturer thereof and/or the requirements of a particular etch process. For example, pressure control rings, hot edge rings, various gas injector nozzles, probes, chamber liners, etc., may also be provided. To simplify the illustration, these well-known components are omitted from FIG. 1.
Generally speaking, it is critical to maintain tight control of the etch process in order to obtain a satisfactory etch result. Thus, parameters such as the RF voltage, RF power, bias voltage, bias power, plasma density, the amount of contamination in the chamber, and the like, must be carefully controlled. In this regard, the design of the plasma processing chamber, and in particular the design of the plasma-facing components, is tremendously important. As the term is employed herein, a plasma-facing component represents a component that has at least one surface exposed to or facing the plasma during processing. In general, the plasma-facing components in the chamber must be carefully selected in order to obtain the desired combination of reasonable cost, appropriate mechanical strength, compatibility with the etch chemistry, low contamination, appropriate electrical properties, and others.
For example, aluminum, anodized aluminum, or one of the aluminum alloys has long been employed to fabricate plasma-facing components. Although aluminum is relatively inexpensive and easy to fabricate, it suffers from chemical incompatibility with certain etch processes, such as those involved in etching aluminum layers on the substrate surface. Even with an anodized coating or some other coatings, the risk of contamination due to the unwanted presence of aluminum-containing particles in the chamber makes aluminum unacceptable in certain applications. Such aluminum-containing particles may cause unwanted deposition of contaminants on the substrate being processed, or may be incorporated into the polymer deposition along the chamber sidewalls, rendering the chamber cleaning task more difficult and more time-consuming to perform.
Other materials such as silicon carbide (SiC) possess different chemical characteristics, and may thus be employed to fabricate plasma-facing components although the use of SiC may involve trade-offs in cost, electrical properties, and/or mechanical properties. Some materials may have the right chemical and electrical properties but may, for example, be very difficult and/or expensive to fabricate and/or to produce with the requisite degree of purity. Thus, no material is perfect for every application, and one that is chemically compatible and results in low contamination often suffers from other deficiencies, such as undesirable electrical properties. Accordingly, manufacturers constantly try to balance various factors in selecting the “right” material for these plasma-facing components for use in different processing applications
It is observed by the inventors herein that at certain RF power settings in certain processes, arcing may occur between the plasma, such as plasma 124 of FIG. 1, and a plasma-facing surface of a plasma-facing component. Arcing appears to occur irrespective of whether the plasma-facing surface is in direct contact with the observable plasma cloud of plasma 124. In some cases, if the plasma-facing component is formed of a material having a relatively low resistivity, arcing appears to be more pronounced during certain phases of the process. These low resistivity materials may include, for example, aluminum, stainless steel, various alloys of aluminum and/or stainless steel, low resistivity silicon carbide (SiC), silicon (Si), boron carbide (B4C), graphite (C), and the like. Low resistivity materials are sometimes favored in the fabrication of certain plasma-facing components, such as the chamber wall, because the low resistivity materials appear to be more efficient at containing the RF energy within the chamber. It is also observed that in certain etch processes that cause polymer deposition on a plasma-facing surface, arcing seems to be more pronounced during certain phases of the process.
Arcing is a serious problem, as it detrimentally degrades the process result. For example, FIG. 2 is a graph of the 431 nm optical emission of the plasma during an exemplary etch process in which arcing is observed. As indicated by the transient spikes 202A and 202B in the optical emission signal, the plasma behaves unpredictably during arcing, thus yielding in an unacceptable etch result. Furthermore, the arcing sometimes sputters particles from the plasma-facing surface into the chamber interior, resulting in unwanted contamination at unpredictable times. Still further, arcing causes damage, often serious damage, either immediately or over time to the plasma-facing surface of the plasma-facing component.
For example, FIG. 3 shows a photograph of the interior surface of a silicon carbide plasma-facing component damaged by arcing. In this case, the pattern of the arc tracks 302 is influenced by the magnetic fields associated with the radially disposed magnets that surround the exterior circumference of the chamber wall. It should be pointed out that the magnets happen to be part of the chamber within which the photograph of FIG. 3 was taken; however, the presence or absence of magnets appears not to be a determinant as to whether arcing would occur. The SiC particles displaced from the chamber wall along the arc tracks are introduced into the chamber interior as contaminants. The pitting caused by arc tracks 302 on the chamber wall interior necessitates chamber wall replacement, which is an expensive and time-consuming process and an unwanted interruption in the utilization of the plasma processing chamber in the production of semiconductor products.
Of course, one obvious approach to control arcing would be to simply ground the plasma-facing component, by connecting the plasma-facing component directly to ground. Despite many attempts, directly connecting the plasma-facing component to ground does not always solve the problem. Another approach to control arcing would be to modify other process parameters, such as the RF voltages and RF powers of the various RF power sources. However, this is not always possible since many processes require that certain parameters be kept within a certain range. Still another approach to control arcing would be to select a material having different electrical properties for the plasma-facing components. However, this is also not always a desirable solution since a different material may introduce a different set of problems, such as incompatible chemical properties, increased contamination, increased cost of fabrication, low mechanical strength, and the like.
In view of the foregoing, there are desired improved methods and apparatus for reducing and/or eliminating arcing between a plasma-facing component associated with a plasma processing chamber and the plasma present during processing. Preferably, the techniques for reducing and/or eliminating arcing would be adaptable to any type of material that may be employed to fabricate the plasma-facing components.